Numerous methods of latent recovery have been developed and implemented resulting in cases being solved that would have been passed over in days past. The Cyanoacrylate Ester (CE) fuming process was developed in the late 1970's and is the most common method of processing currently in use for non-porous materials. Atmosphere CE is a method used to coat latent fingerprint residues with cyanoacrylate ester residue. The process involves an item being enclosed in a chamber, along with a heat source and a humidity source. The heat source is usually a coffee warmer and the humidity source warm water. The water can be introduced with a humidifier or just by placing a jar of warm water into the chamber. The liquid CE is placed into an aluminum weighing tray and heated changing the state from a liquid to a fume. The fume fills the chamber and deposits a white residue on waters and oils on the item. The resulting residue can be dusted with powders, dye stained, or photographed and is permanent until cleaned with acetone.
In the 1980's, CE fuming using Vacuum in a chamber held some promise in the recovery of latent fingerprints on non-porous surfaces. The resulting prints were slight and needed to be dye stained. Advancement to the Vacuum CE fuming technique was introduced in 1989 with the addition of a heating element inside the vacuum chamber enhancing the polymerization of the cyanoacrylate ester (also known as “super glue”), changing the amount of residue on a latent fingerprint and shortening the time needed for processing. Vacuum CE w/HA differs from Vacuum CE in that the CE is vaporized in a quick efficient fashion, similar to the atmosphere process using a hot plate. This allows for a denser concentration of CE particles to be dispersed within the chamber. Since vacuum CE is evenly dispersed in the chamber, increasing the density and number of CE particles results in a thicker deposition of CE on the ridges and no deposit in the valleys. The fact that no deposition occurs in the valleys is common to all vacuum methods. Also common to all vacuum methods is the ability to reprocess an item multiple times. The exception for vacuum CE w/HA when compared to vacuum CE without HA, is that the deposition of CE is much thicker when heated, resulting in having fewer times of processing for a quality latent print.
The history of vacuum cyanoacrylate latent processing is fairly new. It was invented in the 1980's in Canada and spread quickly throughout the forensic community. The chamber consisted of a thick wall PVC pipe with an average inner diameter of about 12-24 inches. An end cap built for the pipe was affixed permanently and an air tight lid was manufactured for the front of the chamber. A valve system was introduced to allow air to be removed from the chamber and sealed to create a vacuum. Items were placed into the chamber for processing along with a tray of liquid cyanoacrylate (CE). Once the chamber was pumped to a complete vacuum, the CE then would boil at room temperature and evaporate into the chamber. The vacuum would then distribute evenly placed spherical molecules of CE throughout the chamber. The molecules would be able to penetrate areas that CE fumes in atmosphere could not. For example, a plastic baggie in an atmosphere chamber would only deposit CE residue on the outer portions of the bag, a vacuum chamber would deposit CE residue on all surfaces of the bag both inner and outer, even if the bag was folded. The resulting print was very light and often powder would not adhere to it, requiring a dye stain to be used. An interesting result was that a latent print recovered using the vacuum CE method could be reprocessed as many times as necessary to build a success latent fingerprint. Since the amount of residue was so light, this method became impractical for everyday use on casework due to the man hours needed. For this reason vacuum CE began to lose favor with latent fingerprint recovery professionals.
In 1989, the present inventor began to experiment with vacuum CE and found the same lackluster results. The present inventor used a desiccator and a small vacuum pump and tried various methods to introduce the CE into the chamber with failed results. That year, the present inventor attended a demonstration of a Vacuum Metal Deposition (VMD) machine and realized that heating elements inside the vacuum chamber were the answer and set about to build a chamber. The present inventor bought a rotary vacuum pump with a 3.5 CFM rating, a three-foot section of sewer pipe with an inner diameter of twelve inches, and an end cap. The end cap was secured to the pipe with epoxy and checked for a good seat. A one-inch thick acrylic lid was machined to fit the front of the pipe with a perfect fit, along with a rubber gasket to create an airtight seal. The lid had a lip cut so as to fit about ⅜ inch into the tank with the remaining on the exterior of the pipe lip. Gas valves and threaded pipe were configured into a three valve inline system so as to allow vacation of atmosphere from the chamber, diversion of suction so the pump can be shut off properly, and the reentry of atmosphere into the chamber through one threaded and sealed port on the rear end cap. A second threaded and sealed port accommodated the vacuum gauge. Two small holes just large enough for wire to be put into the chamber were drilled and a 110 volt extension plug was placed in the interior of the chamber. Those holes were sealed using epoxy and the chamber was ready for testing. Even though the wall thickness was ½ inch, the present inventor was warned to watch for an implosion of the chamber. The present inventor tested the chamber in 1989 with successful results: the chamber held a vacuum for over 6 hours. The present inventor further tested the electricity inside the chamber with a radio. As the atmosphere in the chamber was being pumped down you could hear the radio in the chamber, you could hear the sound from the radio dissipate as sound conducting air was removed from the chamber, and become inaudible indicating that a full vacuum was achieved.
The present inventor tested the heated CE vacuum chamber for latent processing. The first step for the test was to put glass slides in the heated CE vacuum chamber after depositing latent fingerprints on them. The test used a coffee warmer, such as those used with atmosphere-filled latent fingerprint tanks, inside the chamber to heat the CE in the chamber. The next step was to put an aluminum tray on the warmer with about a 1″-1.5″ diameter puddle of liquid CE in the tray. The heated CE vacuum chamber was pumped free of atmosphere and power was provided to the warmer. The process was repeated at varying the times, CE amounts, and pressures. The best results for processing were about forty minutes, with about a 1″-1.5″diameter puddle of CE, and a vacuum of twenty-seven inches.
The present inventor's findings were presented, along with the heated CE vacuum chamber, at a Northern California Laser Users Group in 1989. The heated CE vacuum chamber and the process received great interest from colleagues, other agencies and even the Home Office in England. A physics professor in Texas had concerns of the effect of CE fumes on PVC and stated emphatically that an implosion would occur using this type of device. He never saw the heated CE vacuum chamber, nor contacted the present inventor in any way. He was referring to schedule 40 PVC, used for sprinkler systems, which has a very thin wall and wouldn't even hold a vacuum if it could be made large enough. Sewer pipe is made to withstand great pressures, and consequently great vacuum.
Interest dropped off about the process after that, but the present inventor continued to use it for case work. The present inventor used the heated CE vacuum chamber in the Fresno County Sheriff's Department for 2½ years from 1989 to 1992 and at the Northern Utah State Crime Laboratory for three years from 1992 to 1995. Currently the present inventor teaches forensics at the associate degree level and uses the heated CE vacuum chamber in classroom training. The heated CE vacuum chamber has never been cleaned, except for the acrylic lid, and the only mark of sustained use is a crust over the warmer.
The heated CE vacuum chamber was used on one case in Utah in 1995, where a wax cookie box, “Chips Ahoy”, had been torn in two for use as a target at a homicide scene. The box was collected and evaluated for processing. The cardboard on the interior would be suitable for ninhydrin (a dye), except this process would destroy latent prints on the waxy coating. It was decided process the waxy coating first with vacuum CE with heat acceleration (HA). After the first process, the item was dusted with a yellow fluorescent powder and viewed with an Omichrome1000 Å alternate light source. The process began to show ridge detail and needed to be reprocessed. The item was then reprocessed five more times with increasing detail alter each process. The result was two identified latent fingerprints to two suspects, with arrests and convictions in both individuals.
A few companies, Payton Scientific and Coleman for example, are starting to offer vacuum CE with HA, but they are very expensive and out of the buying ability of most law enforcement agencies. The Coleman unit retails for around $2,000 and the Peyton Scientific unit for about $35,000. The American Society of Crime Laboratory Directors (ASCLD) does not currently recognize vacuum CE with HA, and it will take extensive testing and review procedures to secure certification for any agency to use it.
The atmosphere CE method is in common use for most law enforcement agencies and laboratories. The method involves placing items in an enclosed chamber at one atmosphere and then introducing humidity and CE fumes. The humidity can be introduced as easily as placing warm water into the chamber, or by using a hygrometer and humidifier. The ideal is usually between 70-80% humidity inside the chamber. Too much humidity will cause the CE fumes to stick to the water vapor in the chamber, coating over items and resulting in a white residue over the entire item. Too little humidity will result in a poor quality latent print. CE fumes can be introduced by chemical or heating methods. Chemical methods rely on a chemical action when drops of CE are placed in contact with treated cotton. Heating methods use one of two common heat sources, a coffee warmer (125 degrees) and a hot plate (400-500 degrees). The (preferred method of contact with the heat is an aluminum weighing tray, with liquid CE in direct contact with the heat source. With a coffee warmer, the CE fumes are heated at a slow rate and often an observer can see a light plume of white smoke rising from the dish. Depending on the size of the tank, it can take as little as fifteen minutes to process an item. Using a hot plate polymerizes the CE in a different manner. The CE will heat rapidly and a large cloud of smoke will fill the chamber quickly. This produces a thicker residue height on the ridges and has increased performance in regard to older fingerprints. This method is preferable when you have a very large tank or makeshift chamber.
The drawback of both methods is that humidity is required for both. When humidity fills the chamber and deposits on the item, it deposits on both the ridge and the valley of a latent fingerprint. Most latent prints recovered are composed of sebaceous fluids and less of water content. When humidity is applied, moisture does deposit on the sebaceous ridge detail and enhance the latent print. Humidity, while enhancing a latent ridge detail, also coats the valley, preventing the latent from being processed any subsequent times. If it is processed a second time, the latent print coats white and all ridge detail is lost.
Older latent fingerprints have traditionally not even been processed when the age of the latent fingerprint that has been exposed to a hot environment (i.e. Arizona summer heat) was discovered to be four days or more. It was deemed useless and a waste of time to go through latent processing when the result will be negative. Light latent fingerprints are subject to a similar decision making process. When a light latent fingerprint is discovered, additional processing using atmosphere CE is not possible. Therefore, the only option is to dye stain the CE ridge and hope enough dye is present to be visible using an Alternate Light Source, (ALS). An alternative to this problem is to process the item with vacuum CE w/HA. Light latent fingerprints using this method of processing can be reprocessed many times to enhance CE ridge height. Often even vacuum CE w/HA will not have a successful result on older latent fingerprints.
Normal humidity processes will not work with the vacuum CE w/HA process. You cannot introduce hot water in a vacuum: water needs air to bond to distribute throughout the chamber.
Humidity appears to be the culprit in atmosphere CE processing. When atmosphere CE is done without humidity the results are poor but in some cases, able to be reprocessed. This does not however, give an adequate result on a sustainable basis. Vacuum CE does have the ability to reprocess, but does not leave enough ridge height to accommodate powder dusting. Vacuum CE with heat acceleration (HA) does give the proper ridge height for powder dusting and is able to be reprocessed. In some cases, however, older prints may not be recoverable by just using this method or any other in current use.
Therefore, a need exists for an apparatus and method for improved recovery of latent fingerprints on nonporous surfaces that can recover latent fingerprints that cannot be recovered by prior art means. A need also exists for an apparatus and method for improved recovery of latent fingerprints on nonporous surfaces that can rehydrate latent fingerprints for a vacuum CE with H/A process. A need also exists for an apparatus and method for improved recovery of latent fingerprints on nonporous surfaces that uses an automatic controller and can be automated to reduce the man-hours needed.